#! /opt/alt/python36/bin/python3.6
"""
A demonstration of classes and their special methods in Python.
"""
class Vec:
"""A simple vector class.
Instances of the Vec class can be constructed from numbers
>>> a = Vec(1, 2, 3)
>>> b = Vec(3, 2, 1)
added
>>> a + b
Vec(4, 4, 4)
subtracted
>>> a - b
Vec(-2, 0, 2)
and multiplied by a scalar on the left
>>> 3.0 * a
Vec(3.0, 6.0, 9.0)
or on the right
>>> a * 3.0
Vec(3.0, 6.0, 9.0)
"""
def __init__(self, *v):
self.v = list(v)
@classmethod
def fromlist(cls, v):
if not isinstance(v, list):
raise TypeError
inst = cls()
inst.v = v
return inst
def __repr__(self):
args = ', '.join(repr(x) for x in self.v)
return 'Vec({})'.format(args)
def __len__(self):
return len(self.v)
def __getitem__(self, i):
return self.v[i]
def __add__(self, other):
# Element-wise addition
v = [x + y for x, y in zip(self.v, other.v)]
return Vec.fromlist(v)
def __sub__(self, other):
# Element-wise subtraction
v = [x - y for x, y in zip(self.v, other.v)]
return Vec.fromlist(v)
def __mul__(self, scalar):
# Multiply by scalar
v = [x * scalar for x in self.v]
return Vec.fromlist(v)
__rmul__ = __mul__
def test():
import doctest
doctest.testmod()
test()